Norodom Sihanouk, Cambodia’s late king father and head of state who oversaw the country’s independence from colonial rule, kept friends in far-off places. One of them, a Chilean bookworm with a penchant for letter writing, became his private secretary, official biographer and confidant. It was a rather unlikely amity.

In November 1967, Julio A Jeldres, a teenager in Santiago, wrote a letter in Spanish to the Cambodian Mission to the United Nations in Manhattan that more or less asked, “What is Cambodia?”. Jeldres, the second son of a shoemaker and a history buff, possessed a budding interest in the world beyond the Andes and had sent similar queries to Thai and Laotian embassies.

Cambodia was a new curiosity. Jacqueline Kennedy’s recent visit to Phnom Penh had been heavily covered in Chile, and the news had piqued the clever high schooler’s interest in the faraway kingdom.

A few months later, Jeldres received a reply. “The King has been informed that you are interested in his country. He is very happy and grateful that a person from Chile has taken interest in Cambodia,” read the hand-scripted letter. “Please believe in my unalterable affection, Norodom Sihanouk”. That was how Jeldres became pen pals with the king of Cambodia.

Over the next three decades, Jeldres and Sihanouk (whose title often changed over the decades) would exchange well over 100 letters and telegrams. It was a period that covered the most consequential scenes of Cambodian history. Jeldres, a relative nobody 17,000 kilometres away, found himself, through pure happenstance, to have a personal audience with its leading actor. The transoceanic correspondence would eventually lead to Jeldres being appointed Sihanouk’s private secretary.

“I never thought that this letter that I sent to the Cambodian Mission to the UN was going to completely change my life,” Jeldres reminisced this week. “But it did.”

Jeldres, a large, bespectacled man with a snow-white beard, black caterpillar eyebrows and prone to giggles, was working through an omelette at a French bistro in Phnom Penh. On the table lay a folder containing several of the letters laminated in pristine condition. A few hundred metres away stood the 27-metre-tall bronze statue of his former pen pal.

After their first exchange, Jeldres reiterated in a second letter his desire to know more about Cambodia. He soon learned that the monarch could be excessive.

Three weeks later, to the horror of the boy’s mother, a truckload of books on Cambodia with multiple copies of each volume, music records and a Cambodian flag arrived at his doorstep.

Jeldres strung the flag to a pole in his backyard, donated most of the books to the library and searched for a language school; the then-prince wrote in French. From 1967-70, Jeldres wrote Sihanouk “at least once a month”.

“I think my initial letters were to support the King’s efforts to keep Cambodia free from involvement in the Vietnam War,” he said.

Initially, the prince’s responses were often stalely formal, but he always replied. The letters from both ends went through the UN mission in New York and took about two weeks to be delivered. Jeldres’ French teacher helped the 16-year-old draft his replies.

Meanwhile, Jeldres nurtured an obsession. He formed a student group, the Friends of Cambodia, and campaigned for the Chilean government to recognise Cambodia’s contested borders, per Sihanouk’s outlining (eventually it did, said Jeldres).

He sent letters to the Cambodian queen, Cambodian diplomats and the current Cambodian king, Norodom Sihamoni, who was studying in Prague.

When an Australian diplomat and friend of Sihanouk was transferred from Phnom Penh to Santiago in 1969, Jeldres invited him to his house for dinner. The ambassador, Noel Deschamps, fielded all of Jeldres’ questions.

“He was a very generous person,” remembered Jeldres. “He taught me a lot about Cambodia.”

Deschamps fuelled the young Chilean’s curiosity. He gave slideshow lectures on Cambodia to Jeldres and his student group at his office at the Carrera Hotel. On Australian National Day, Deschamps hosted a garden party and invited Jeldres and his family to his home, which Jeldres remembered was adorned with Cambodian paintings and statues.

In hindsight, some of the letter exchanges seem prophetic. When Toch Kham Doeun, Cambodia’s left-leaning ambassador to Cuba, visited Chile in 1969, Jeldres met the Cambodian diplomat who told him: “If things come to the worse in Cambodia, the King will not be a head of state,” recounted Jeldres.

The teen took his remark as a warning and drafted a long, worried letter to his royal pen pal. This week, he brought the letter to the French bistro. He also had Sihanouk’s half-century-old response, which he read aloud.

“Please excuse me if I have not sent you messages for some months,” Sihanouk said. “As far as your suspension of support for the FUNK and the GRUNC [Cambodia’s foreign missions] I cannot but approve of you.”

Jeldres’ warning that Sihanouk’s grip on power was weakening turned out to be prescient. A year later, Sihanouk was overthrown in a coup while en route to Beijing (when the Khmer Rouge took over, ambassador Doeun returned to Cambodia to serve in the Foreign Ministry. Two years later, he was arrested, tortured and executed).

In 1972, Jeldres acquired a migrant visa to Australia with help from Deschamps, he said. He left Chile, leaving behind all but his most cherished letters.

A year later, there was another coup, but in Chile. President Salvador Allende was sacked by an army strongman named Augusto Pinoche. The country became a police state. Jeldres would not return home for 17 years.

In Australia, Jeldres went to university and eventually landed a job working with Victoria’s state government. He kept up his correspondence with Sihanouk, who lived in exile in Beijing. Sometimes, the estranged king asked for favours.

When a journalist wrote an article in The Age newspaper claiming that the royal family was being forced to study Maoism in China, Sihanouk asked Jeldres to write a letter to the editor on his behalf denying the claims. He did and they published it.

Eight months after the Khmer Rouge took Phnom Penh in April 1975, Sihanouk returned to Cambodia. He thought he would rule as head of state but instead was kept in his palace under house arrest, powerless as his country imploded around him.

And as Cambodia became a black hole under Pol Pot, so too did Jeldres’ correspondence with the imprisoned monarch, whose only connection to the outside world was a one-way radio. The letters stopped for four years.

Then, in 1981, Jeldres told Sihanouk in a letter that he was going on a trip to Hong Kong. Sihanouk countered with an invitation to come to Pyongyang, where the monarch had a personal residence.

Jeldres went to meet his pen pal for the first time. He was nervous. “To meet a prince, a king – I was a very ordinary person,” Jeldres recalled. After North Korea, the monarchy absorbed him.

For the next 12 years, Jeldres worked under the king’s private secretariat, eventually becoming head of the wing. Initially, he was based in Bangkok but travelled often to Beijing, where Sihanouk had once again taken up residence following Hanoi’s invasion of Cambodia in 1979.

Jeldres lived there permanently for three years, in the king’s Beijing residence, taking notes at meetings, scheduling appointments, drafting letters. They interacted as friends, too. Jeldres recalls watching American films with the movie-buff king, loaned to him by the late North Korean dictator Kim Jong-Il.

In 1992, a year after Sihanouk had returned to Phnom Penh following the Paris Peace Agreements, Jeldres was appointed the royal family’s official biographer. Jeldres spent much time with Sihanouk here while working on his book The Royal House of Cambodia (2003).

Jeldres has been, at times, a controversial figure. In the pages of this newspaper (along with other publications), he has butted heads with Cambodia scholars, often with venom. Tussles have been had over subjects ranging from the genocide to contemporary politics.

In one 1996 op-ed, historian Michael Vickery referred to Jeldres as “incoherent and hysterical” and “a hatchet-wielding assassin of character”. Genocide scholar Ben Kiernan, in his book Genocide and Resistance (2007), paints Jeldres as both a Pol Pot and Pinochet supporter.

Jeldres, for his part, has accused Vickery of instigating “a systematic campaign of denigration” against him, while labelling Kiernan a Khmer Rouge sympathiser, having initially gone “out of [his] way to defend Pol Pot”. The back-and-forths go on and on.

But at the French bistro, Jeldres seemed relaxed and wholly unthreatening. Now a visiting scholar at Monash University under the tutelage of Cambodia scholar David Chandler, he was in town this week to update The Royal House of Cambodia as well as conduct research for a new project, a biography of the late Australian ambassador Noel Deschamps.

He reflected on the past shouting matches with laughter and said he planned on leaving scholarship after his ongoing projects were done. Then his cellphone rang.

“Hello… how are you excellency? I’m fine.” He talked for a couple minutes and hung up. It was the monarch’s private secretary. “The King is calling for me,” he said cheerfully.

Later that afternoon, he went to the Royal Palace and met with Norodom Sihamoni, his old friend, the son of his one-time pen pal, the King of Cambodia.

“But only briefly,” he said. “Not for very long.”